Intensifying screen for radiograph use

ABSTRACT

Disclosed is an intensifying screen for X-ray radiograph use having a striped or checkered pattern of metal strips embedded in a high-sensitive phosphor layer, thereby reducing &#39;&#39;&#39;&#39;mottles&#39;&#39;&#39;&#39; which are offensive to the eye in examining an X-ray picture and at the same time absorbing the scattered X-ray in the screen. The combined effects of reduction of &#39;&#39;&#39;&#39;mottles&#39;&#39;&#39;&#39; and absorption of scattered X-rays improve the image quality of an X-ray picture.

United States Patent Fujimura et al.

INTENSIFYING SCREEN FOR RADIOGRAPH USE Inventors: Ikuo Fujimura; Masao Takano, both of Ashigarakami-gun, Kanagawaken, Japan Fuji Shashin Film Kabushiki Kaisha, Ashigarakami-gun, Kanagawa-ken, Japan Filed: March 5, 1970 Appl. No.: 16,756

Assignee:

Foreign Application Priority Data March 7, 1969 Japan ..44/17260 Oct. 18, 1969 Japan ..44/83338 US. Cl. ..250/80, 250/71 R Int. Cl. ..H0lj 1/62 Field of Search ..250/80, 71 R, 71.5 R;

References Cited UNITED STATES PATENTS 3/1958 Klasens et a1 ..250/8O 1 Feb. 20, 1973 3,089,956 5/1963 Harper ..250/8O 3,344,276 9/1967 Balding ..250/80 2,459,693 1/1949 Gordon ..250/71 R 2,829,264 4/1958 Garrison ..250/80 X 2,975,966 3/1961 Howard ..250/71 R X 3,041,456 6/1962 MacLeod ..250/80 3,043,710 7/1962 Patten et a1 ..250/80 X 3,504,212 3/1970 Wollentin et al. ,.250/80 X Primary Examiner-James W. Lawrence Assistant ExaminerDavis L. Willis Att0rneyStevens, Davis, Miller & Mosher [57] ABSTRACT Disclosed is an intensifying screen for X-ray radiograph use having a striped or checkered pattern of metal strips embedded in a high-sensitive phosphor layer, thereby reducing mottles which are offensive to the eye in examining an X-ray picture and at the same time absorbing the scattered X-ray in the screen. The combined effects of reduction of mottles and absorption of scattered X-rays improve the image quality of an X-ray picture.

17 Claims, 17 Drawing Figures PATENTEDFEB20|923 I 717, 764

SHEET 10F 3 RESPONSE R (u) 0 IO 20 30 40 5 0 SPATIAL FREQUENCY u('-4 FIG.3

IKUO FUJIMURA MASAO TAKANO INVENTORS ATT PATENIEDFEBwQIa sum 2 or 3 FIG.6

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IKUO FUJIMURA MASAO TAKANO INVENTORS AT ORNEYS PATENTEBFEBZOIHYS 3,717 764 sum 30F 3 IKUO FUJIMURA MASAO TAKANO INVENTORS ATTORNEYS INTENSIFYING SCREEN FOR RADIOGRAPH USE This invention in general, relates to a luminescent or intensifying screen for radiograph use, and in particular to such an intensifying screen which permits the full use of a relatively high sensitivity radiographic film or particularly, an X-ray photographic film by compensating for the reduction of sharpness accompanied by allowing the X-ray to pass through luminescent or phosphor layers and thereby intensifying the light which is used to produce an image on the photographic film.

In the conventional art of taking a radiograph or an X-ray photograph for a medical diagnosis, a lamination consisting of a radiographic or X-ray photographic film and two intensifying screens laid on both surfaces of the radiographic film is used.

A radiographic or X-ray film comprises a support or carrier of whose surfaces have an emulsion applied thereto. An intensifying screen is a plate having granulated phosphor crystal applied to one surface thereof by means of a proper binder such as nitrocellulose, gelatine, etc.

The sharpness and the granularity of the radiographic film are, in fact, of a satisfactory figure of merit, as is commonly admitted in the art. However, an intensifying screen laid on an X-ray film tends to intensify the light which is used to produce an image on the film, but unfortunately also tends to deteriorate the sharpness of the image appearing in the film, to ten times lower than the sharpness of the corresponding image of an X-ray photograph taken without using an intensifying screen. This adverse effect caused by the use of the intensifying screen will increase with the intensifying factor of the screen used.

Additionally the scattering of an X-ray caused by the presence of the intensifying screen tends to deteriorate the sharpness of the image.

Almost all the causes for lowering the quality of an image appearing on the film are found in the X-ray emission tube and the intensifying screen. Stated otherwise, in order to improve the quality of the image of the X-ray photograph, it is best to improve the X-ray emission tube and/or the intensifying screen.

Referring to FIG. 3, it shows different response-tospatial frequency relationships pertaining to an X-ray source having 300 X 300 pt dimensions (See curve a), and X-ray photographic film having an emulsion applied to one surface thereof and an X-ray source having 50 p. X 50 a focus dimensions (See curve b), a conventional high sensitive intensifying screen (See curve c), and finally an X-ray photographic film having an emulsion applied to both surfaces thereof (See curve d). As seen from this graphic representation the response of the conventional intensifying screen is very poor.

As is apparent from this fact, the improvement of the response of the intensifying screen will substantially contribute to improve the whole or resultant response of the X-ray photographic system including an X-ray source, an X-ray photographic film, an intensifying screen etc.

This invention is directed to improve one of the major factors above mentioned, i.e., the intensifying screen.

The object of this invention is, in general, to improve the quality of the image of the X-ray photograph taken with the use of an intensifying screen. This object is attained by embedding a number of metal strips in the phosphor coating in a striped or checkered pattern, thereby first, dividing a mottle or an image of agglomeration of phosphor grains into a group of small sections which are not offensive to the eye of the observer in examining the X-ray photograph, and second, absorbing the scattered X-ray in the metal grid of the phosphor coating, thus confining the luminescence glow in the very small region defined by the mesh of the grid.

As seen from the above, this invention permits the use of phosphor material of high sensitivity by reducing relatively large mottles inherent to such material to the extent that they may not be offensive to the eye, thus improving the sensitivity of the intensifying screen without lowering the sharpness of the image of the X- ray photograph.

The advantages of this invention are listed below:

I. The granularity is substantially improved by dividing the image into fine stripe or minute square sections.

2. The sharpness is improved by absorbing the scattered X-rays with the metal strips.

3. The detecting capability i.e., signal-to-noise ratio is improved as a consequence of above items I and 2.

4. The sensitivity is increased, because a high sensitive phosphor material can be used without the adverse effect of lowering the granularity and the sharpness.

This invention will be better understood from the following description which is made with reference to the accompanying drawings in which:

FIG. 1 is a plan view showing a part of the striped pattern type intensifying screen according to this invention;

FIG. 2 is a plan view showing a part of the checkered pattern type intensifying screen according to this invention;

FIG. 3 is a graph showing spatial frequency-response function relationships pertaining to different X-ray films and X-ray sources;

FIG. 4 is a graph showing the relationships between the width W of metal strip and the number N of metal and phosphor strip pairs per millimeter and between the width W of metal strip and the relative sensitivity S of the phosphor screen;

FIGS. 5 7 show examples of one type of this invention;

FIGS. 8 17 show examples of a different type of this invention.

Referring to FIG. 1, a part of the stripe type intensifying screen is shown. This screen is shaped in the form of arranged phosphor and metal strips 1 and 2 in an alternate and equi-spaced fashion.

Assuming that the width of the metal strip W is equal to that of the phosphor strip W,, this is given in the following equation:

wherein N (lines/mm) indicates the number of pairs of metal and phosphor strips per millimeter. The relative sensitivity S" of the stripe type intensifying screen (i.e., the sensitivity ratio of the stripe type phosphor coating to the plain phosphor coating) is given in the following equation:

S l N W Referring to FIG. 2, a part of the checker type intensifying screen is shown. This screen is shaped in the form of arranged metal and phosphor strips 1 and 2 in a checkered and cqui-spaced fashion. Assuming that the width of the metal strip W is equal to that of the phosphor strip W,, the area A of the square section of the phosphor coating is given in the following:

The relative sensitivity S of the checker type intensifying screen (i.e., the ratio of the sensitivity of the checkered phosphor coating l/N) to that of the plain phosphor coating l/N W is given by the following equation:

In order to take a photograph of a fiber so clear that the filaments per millimeter are easily detectable to the eye, the response function of the intensifying screen must be lines per millimeter.

If the width of the phosphor strip 2 of the stripe type intensifying screen is equal to that of the metal strip 1, and if the number of the phosphor strip 2 is 20 lines per millimeter, the width of the phosphor strip 2 is given by:

FIG. 4 shows how the relative sensitivity S" or S varies withthe width of the metal strip. These curves S" and S are determined by the equations and S# WM)Z for the particular width of the phosphor strip, i.e.,

W IL.

As seen from FIG. 4, the relative sensitivity increases with the decrease of the metal strip width. For the particular sensitivity, i.e., one-half, the width W,, of the metal strip of the stripe type intensifying screen is about ,u., whereas the width of W,, of the metal strip of the checker type intensifying screen is about 10 a. As for the number of the stripe (phosphor or metal stripe) per millimeter for one-half relative sensitivity, the stripe number of the stripe type intensifying screen is about 19 (lines/mm), whereas the stripe number of the checker type one is about 28 (lines/mm).

The decrease of the sensitivity due to the stripe or checker pattern of metalstrips, however, is compensated by using a phosphor material of high sensitivity, because the mottle problem inherent to such a high sensitive phosphor material is solved by the metal grid, as hereinabove mentioned.

The ratios of phosphors of medium and high sensitivity commercially available to the phosphor of low sensitivity and high sharpness are 1.6 and 2.4 respectively. As is well known, a conventional intensifying screen uses a phosphor of low sensitivity and high sharpness. This is due to the fact that the sharpness and the granularity of a phosphor of higher sensitivity is, in

fact, lower than the sharpness and granularity of a phosphor of lower sensitivity. The sharpness and granularity of the intensifying screen according to this invention depends simply upon the size of the elemental mesh of the metal net pattern, and not on the actual phosphor and granularity of the phosphor material. Thus, the decrease of the sensitivity due to the metal stripe or checker pattern can be fully compensated by the use of a highly sensitive phosphor material, provided thatthe area which the phosphor material occupies is, in fact, larger than the area which the metal occupies.

Referring to FIG. 5, the section of an intensifying screen is shown. A number of metal strips 1 are laid upon the support member or carrier plate 3 in an equispaced relationship and a phosphor material 2 is moulded between the metal strips so that the resultant phosphor strips may be flush with the metal-strips. A protecting coating 4 is applied to the upper surface of the stripe pattern. FIGS. 6 and 7 show an intensifying screen having respectively trapezoid-sectional metal strips and one having corrugated metal strips. The distances indicated by W, and W depend upon the kind of object and characteristics of the camera used, but such distances will be found in the following ranges:

T 1O 300p.

W, 1 l0 200p.

The light released from the intensifying screen increases with the thickness T of the phosphor coating until it reaches a definite value, which remains constant even though the thickness of the phosphor layer may further increase. In view of this saturating nature, the minimum phosphor layer thickness beyond which the increase of the available light ceases, is chosen for the proper thickness of the phosphor coating. Such a value, however, depends on the kind of phosphor material or binder used in the intensifying screen. The support member 3 is a sheet made of cellulose triacetate, polyethylene terephthalate, phenol resin, acrylic resin, etc.. The support member 3 must have a strength sufficient to support the phosphor part and the metal part, the latter of which is preferably made of a metal having a large X-ray-absorbing capability, more specifically a heavy metal having a large figure of atomic numbers. The protecting coating 4 is preferably made of a material with light transparent characteristics and substantial physical strength, such as gelatine, polyvinyl alcohol, cellulose triacetate, etc.. The coating 4 is preferably as thin as possible, and the thickness of the coating is generally within the range from 1 to 10 microns.

As for the phosphor material and binder, they are well known in the art, and therefore no detailed explanation is needed. 7

F I08. 8 17 show embodiments of a different type of this invention, in which the upper end of a metal strip reaches short of the upper or lower surface of the phosphor moulding. In these figures the same type of members are indicated by the same numbers as used in FIGS. 1 and 2.

FIG. 9 shows an intensifying screen having a light reflecting layer (or a light-absorbing layer) 5 provided on the support 3.

FIG. shows an intensifying screen having a metal coating 6 provided on the metal strip 1, the atomic number of the metal of this metal coating 6 being larger than that of the metal of the metal strip with a view to further absorb the scattered X-ray.

FIGS. 11 13 show intensifying screen in which the metal strips are partly embedded in the support as indicated at T thereby intensifying the absorbing effect of the scattered X-rays.

FIG. 14 shows the section of the intensifying screen having the metal strips provided flush with the phosphor moulding, and FIG. 15 shows one having the metal strips provided at the middle level of the phosphor moulding. The dimensions indicated by T, and T are found in the following ranges:

W =5200p., where T, is equal to T,, +T,"

As for the light-reflecting or light-absorbing layer 5, it is formed by applying titanium white to the surface of the support or by evaporating a metal such as aluminum, silver, etc. to the same, thus functioning as a reflector for a low-sensitive intensifying screen, whereas it is formed by applying a light-absorbing substance, for instance carbon to the surface of the support with a view to improve thesharpness, thus functioning as an absorber for a high-sensitive intensifying screen, just like a halation protecting layer on radiographic films.

FIGS. 16 and 17 show phosphor screens using two different kinds of phosphor material constituting two different phosphor layers with a view to improve the granularity of the intensifying screen. As mentioned earlier, the use of a high sensitive (or coarsely granulated) screen is necessitated in order to compensate for the decrease of sensitivity due to the presence of the metal strips in the phosphor coating. The granularity can be improved by applying a low-sensitive phosphor material on the high-sensitive and coarsely granulated phosphor layer 2, provided that the upper layer 2 of a low-sensitive phosphor material is thinner than the lower layer 2' of a high-sensitive phosphor material, preferably three times or more thinner than the lower phosphor layer. For similar purposes, a tricomposite phosphor layer, or a phosphor layer of a mixture of different phosphor materials can be applied to the support.

In making an intensifying screen according to this invention, a metal layer is deposited on a carrier by electroplating, for instance, copper on the surface of the carrier, and then the metal layer thus deposited is partly removed to leave a striped or checkered pattern by photoetching with or without electroplating, electrical discharge machining or laser machining. Then, a liquid containing phosphor material is applied to the striped or checkered metal pattern.

Alternately, a striped or checkered pattern is formed by depositing metal particles on a carrier by printing or xeroprinting, and then, a liquid containing a phosphor material is applied to the striped or checkered metal pattern thus formed. This method is particularly suitable for making intensifying screens, such as shown in FIGS. 5, 6, 7, 8, 9 and l0.

Likewise, an intensifying screen according to this invention can be produced by embedding in a luminescent layer, a metal mesh or a perforated metal foil of the type which is used in spectrophotometry. The metal mesh can be produced by the reprica method or etching. The liquid containing a phosphor material is applied on the carrier, and then the metal mesh is put in the luminescent layer thus deposited, while it is wet. The wet luminescent layer which is flush with the metal pattern, is dried and solidified. If this intermediate product is covered with a protecting coating, an intensifying screen, such as shown in FIG. 14 can be obtained, whereas if another wet luminescent layer is applied to the intermediate product above mentioned, and if this second luminescent layer after it is dried, is covered with a protecting coating, an intensifying screen such as shown in FIG. 15 can be obtained. In producing intensifying screens, such as shown in FIGS. 11, 12 and 13, it is advantageous to embed a metal pattern in a carrier before applying a luminescent layer to the carrier.

Although the invention has been described hereinbefore with reference to some specific embodiments thereof, it will be understood that many modifications are possible within the scope of the invention as set forth in the appended claims.

What is claimed is:

1. An intensifying screen for radiograph use comprising a support, a layer of finely divided luminescent crystals deposited on said support and metal dividing means dividing said luminescent layer into a plurality of separated sections, said metal dividing means comprising a plurality of metal strips disposed in the luminescent layer, said metal strips having a longitudinal dimension T and a width W the sections of said luminescent layer having a longitudinal dimension T, and a width W,, the aforementioned dimensions being within the following ranges:

T, l0 300p.

W, l0 200p. thereby dividing an image of agglomeration of Inminescent crystal grains into small sections which are not offensive to the eye of an observer examining the radiograph.

2. An intensifying screen according to claim 1, wherein said metal dividing means comprise a plurality of metal strips embedded in the luminescent layer in a striped pattern.

3. An intensifying screen according to claim 1, wherein said metal dividing means comprise a plurality of metal strips embedded in the luminescent layer in a checkered pattern.

4. An intensifying screen according to claim ll, wherein said metal dividing means comprise a perforated metal foil embedded in the luminescent layer.

5. An intensifying screen according to claim 1, further comprising a light-reflecting layer provided on said support between said carrier and said luminescent layer.

6. An intensifying screen according to claim 1, further comprising a light absorbing layer provided on said support between said support and said luminescent layer.

7. An intensifying screen according to claim 1, wherein said metal dividing means comprise metal strips which are rectangular in cross section.

8. An intensifying screen according to claim 1, wherein said metal dividing means comprise metal strips which are trapezoidal in cross section.

9. An intensifying screen according to claim 1, wherein said metal dividing means comprise metal strips which are corrugated in cross section.

10. An intensifying screen according to claim 1, wherein said. metal dividing means comprise metal strips embedded flush with the upper surface of said luminescent layer.

11. An intensifying screen according .to claim 1, in which said luminescent layer comprising a lamination of an upper layer of finely divided crystals and a lower layer of coarsely divided crystals.

12. An intensifying screen according to claim 1, in which said luminescent layer comprising a layer of a mixture of different luminescent materials.

13. An intensifying screen according to claim 1, in which a protective coating is provided on the luminescent layer.

14. An intensifying screen according to claim 13, in which the protective coating is made of a member selected from the group consisting of gelatine, polyvinyl alcohol or cellulose triacetate.

15. An intensifying screen according to claim 14, in which the thickness of the protective coating is within the range from 1 to 10 microns.

16. An intensifying screen for radiograph use comprising a support, a layer of finely divided luminescent crystals deposited on such support, metal dividing means dividing said luminescent layers into a plurality of separated sections, and a metal coating provided on said metal dividing means, the atomic number of the metal coating being larger than that of the metal dividing means, said sections being of a size small enough to divide an image of agglomeration of luminescent crystal grains into small sections which are not offensive to the eye of an observer examining the radiograph.

17. An intensifying screen for radiograph use comprising a support, a layer of finely divided luminescent crystals deposited on said support, and metal dividing means dividing said luminescent layer into a plurality of separated sections, said metal dividing means comprising metal strips, and in which the thickness of the luminescent layer T, the width of each section W, and the width of the metal strips W are within the following ranges:

T 1 10 300 w,; 10- 200 w, 1 5 100,,

thereby dividing an image of agglomeration of luminescent crystal grains into small sections which are not offensive to the eye of an observer examining the radiograph. 

1. An intensifying screen for radiograph use comprising a support, a layer of finely divided luminescent crystals deposited on said support and metal dividing means dividing said luminescent layer into a plurality of separated sections, said metal dividing means comprising a plurality of metal strips disposed in the luminescent layer, said metal strips having a longitudinal dimension TM and a width WM, the sections of said luminescent layer having a longitudinal dimension TI and a width WI, the aforementioned dimensions being within the following ranges: TM : 10 - 300 Mu WM : 5 - 200 Mu TI : 10 - 300 Mu WI : 10 - 200 Mu thereby dividing an image of agglomeration of luminescent crystal grains into small sections which are not offensive to the eye of an observer examining the radiograph.
 2. An intensifying screen according to claim 1, wherein said metal dividing means comprise a plurality of metal strips embedded in the luminescent layer in a striped pattern.
 3. An intensifying screen according to claim 1, wherein said metal dividing means comprise a plurality of metal strips embedded in the luminescent layer in a checkered pattern.
 4. An intensifying screen according to claim 1, wherein said metal dividing means comprise a perforated metal foil embedded in the luminescent layer.
 5. An intensifying screen according to claim 1, further comprising a light reflecting layer provided on said support between said carrier and said luminescent layer.
 6. An intensifying screen according to claim 1, further comprising a light absorbing layer provided on said support between said support and said luminescent layer.
 7. An intensifying screen according to claim 1, wherein said metal dividing means comprise metal strips which are rectangular in cross section.
 8. An intensifying screen according to claim 1, wherein said metal dividing means comprise metal strips which are trapezoidal in cross section.
 9. An intensifying screen according to claim 1, wherein said metal dividing means comprise metal strips which are corrugated in cross section.
 10. An intensifying screen according to claim 1, wherein said metal dividing means comprise metal strips embedded flush with the upper surface of said luminescent layer.
 11. An intensifying screen according to claim 1, in which said luminescent layer comprising a lamination of an upper layer of finely divided crystals and a lower layer of coarsely divided crystals.
 12. An intensifying screen according to claim 1, in which said luminescent layer comprising a layer of a mixture of different luminescent materials.
 13. An intensifying screen according to claim 1, in which a protective coating is provided on the luminescent layer.
 14. An intensifying screen according to claim 13, in which the protective coating is made of a member selected from the group consisting of gelatine, polyvinyl alcohol or cellulose triacetate.
 15. An intensifying screen according to claim 14, in which the thickness of the protective coating is within the range from 1 to 10 microns.
 16. An intensifying screen for radiograph use comprising a support, a layer of finely divided luminescent crystals deposited on such support, metal dividing means dividing said luminescent layers into a plurality of separated sections, and a metal coating provided on said metal dividing means, the atomic number of the metal coating being larger than that of the metal dividing means, said sections being of a size small enough to divide an image of agglomeration of luminescent crystal grains into small sections which are not offensive to the eye of an observer examining the radiograph. 